how to get author url

<?php
function topauthors() {

$uc=array();

$blogusers = get_users_of_blog();

if ($blogusers) {

foreach ($blogusers as $bloguser) {

$post_count = get_usernumposts($bloguser->user_id);

$uc[$bloguser->user_id]=$post_count;

}

arsort($uc); //use asort($uc) if ascending by post count is desired

$maxauthor=10;

$count=0;

foreach ($uc as $key => $value) {

$count++;

if ($count <= $maxauthor) {

$user = get_userdata($key);

$author_posts_url = get_author_posts_url($key);

$post_count = $value;

echo ‘ ‘ . $user->user_firstname . ‘ ‘ . $user->user_lastname .'(RSS) (‘. $post_count. ‘)’;

}

}

}

}

?>

i am using this code for top 10 authors it is working but i didnt get authors url. and i dont wana use plugin so any one kindly help me regarding this.

my website is https://www.chowrangi.com

i need top 10 authors by post and there url.